In a conventional motor, a magnet is mounted on an end portion of a shaft of a rotor, a magnetic sensor is opposed to the magnet on an axis of the shaft, and a rotation angle of the rotor is detected by measuring the magnetism of the magnet using the magnetic sensor, whereupon the motor controls a current supplied to a stator winding. In this type of conventional motor, when a conductor wire through which a current flows, for example, is disposed on the periphery of the magnetic sensor, a noise magnetic field generated by the conductor wire acts on the magnetic sensor, leading to an increase in the likelihood of a detection error occurring when the magnetic sensor detects the magnetism.
In a motor proposed in the prior art with the aim of suppressing detection errors by the magnetic sensor, first and second conductor wires through which currents of the same phase flow are disposed in symmetrical positions relative to the axis of the shaft, with the result that noise magnetic fields generated respectively by the first and second conductor wires cancel each other out in the position of the magnetic sensor (see PTL 1, for example).
In another motor proposed in the prior art with the aim of suppressing detection errors by the magnetic sensor, the magnet and the magnetic sensor are surrounded by a substrate holder made of magnetic metal so that a noise magnetic field from the periphery of the magnetic sensor is blocked by the substrate holder (see PTL 2, for example).